1. Field of the Invention
The present invention relates to a motor controller included in a positioning apparatus for a semiconductor manufacturing apparatus, a machine tool, or an industrial robot. More specifically, the present invention relates to a motor controller with which a gain margin can be simply evaluated by adding a sweep sine wave to a driving force as a disturbance signal and detecting an oscillation of a feedback loop of a control unit on the basis of a first threshold based on the magnitude of vibration and a second threshold based on a vibration frequency.
2. Discussion of the Background
A method for extracting a limit gain of a servo control apparatus according to a related art is described in, for example, Japanese Unexamined Patent Application Publication No. 2005-45937. According to this method, to extract a limit gain of a servo control apparatus capable of automatically setting an optimum control gain, the servo control apparatus is provided with vibration detecting means and vibrating means which adds a simulated disturbance torque to a torque command. The simulated disturbance torque generates vibration of a certain level when a control gain is increased. Processes of applying vibration after making an adjustment, causing the vibration detection means to detect the vibration, and adding the simulated disturbance torque while increasing a control gain unless vibration of a certain level is detected are repeated, and a control gain at which vibration with a level that exceeds the certain level is detected is determined as the limit gain. A maximum gain is determined in advance, and the control gain is set below the maximum gain.